Technical Field
The present invention generally relates to nanochannel devices and methods for making the same, and more particularly to methods and devices with reproducible nanogaps formed between electrodes within the nanochannel.
Description of the Related Art
On-chip electrodes can be incorporated into lab-on-a-chip (LOC) or micro total analysis systems (μTAS) to perform several functions, such as sorting of charged biological material, electrokinetic driving of the same to induce flow in a specific direction, or for sensing biomolecules by transducing events into electrical signals when electrodes are configured in a nanogap arrangement. In the latter case, the electrode tips need to be in close proximity to detect nanoscale (<100 nm) biocolloids of broad interest to biotechnology companies and academics alike, such as DNA, exosomes, viruses, protein aggregates, etc.
The use of noble metals as the electrode material is desirable to avoid irreversible modification processes, such as oxidation, of the electrodes as the electrodes interface with the microfluidic environment; however, these materials are extremely difficult to pattern, particularly at nanoscale dimensions.
Control over nanogap dimensions has employed He ion beams to cut noble metal nanowires into a set of nanogap electrodes and even within nanochannels. However, use of a He beam to cut precision gaps requires labor intensive manual operation to align and cut the gaps (i.e., relatively low throughput), and the noble metal splatters locally during the cut redistributing metal around the incision that may have deleterious effects on the surface of the channel close to the proximity of the gap. This ultimately impedes or completely restricts fluid flow through the detection device.
Additionally, He beam cutting on SiO2 over silicon causes swelling of the silicon, which further complicates analysis. Besides angled deposition techniques and He beam cutting to form a nanogap in metal electrodes, self-aligned sacrificial metal, electromigration, or dry/wet etching approaches have also been employed to form a gap, but all of these methods result in low process control, large nanogap variation, and/or low yield.